1. Field of the Invention
The present invention relates to a wind turbine, in particular to a wind turbine having the wind turbine hub supported directly by the main frame, such that the transmission of torque from the hub to the generator is separated from the support of the rotor.
2. Description of Related Art
Rotor support-type wind turbines are a known alternative wind turbine design, wherein the structural load of the hub and rotor blades is provided by a fixed support shaft provided on the wind turbine main frame. As the hub is allowed to rotate freely about the support shaft, consequentially the structural load is transferred to the main frame while the torque provided by the spinning rotor blades is transferred to the generation system.
U.S. Pat. No. 4,757,211 discloses a rotor support-type wind turbine wherein a rotor hub is mounted onto a cylindrical section of the machine housing, the structural load of the rotor hub being supported by the machine housing. A hub shaft extends from the hub to the gearbox, and is accordingly coupled to the generator.
One of the disadvantages of such a system is that in order to compensate for vibrations and bending moments transferred through the hub shaft from the hub, the generator and the gearbox must be mounted on vibration damping elements which are coupled to the machine housing. Furthermore, the hub is mounted to the machine housing utilising flexible bushings and further damping elements. Damping elements can also used in such constructions to compensate for misalignments between turbine components, e.g., in the case of the hub shaft and the gearbox not being perfectly aligned.
Such damping elements are subject to wear and tear during the lifetime of the system, often requiring replacement every 3-5 years in a relatively costly maintenance operation, at which time the turbine must be taken out of service for an extended period of time.
Additionally, the presence of dampers in the turbine system introduces a variable element to turbine modelling, in that it can be hard to predict where the most stresses on the other turbine components will occur, due to the unpredictability of the performance of the damper elements.